1. Technical Field
The present invention relates in general to an improved data processing system and in particular to a method and system for enhanced projection of data processing system generated text, graphics or multimedia presentations. Still more particularly, the present invention relates to a method and system for precompensating data processing system generated text, graphics or multimedia presentations to compensate for distortion resulting from off-axis projection.
2. Description of the Related Art
As the availability of desktop publishing and graphic presentation software increases, and as such software becomes easier to utilize, the public is beginning to expect a higher standard of quality in the communication of information through the text, graphics and multimedia presentations produced utilizing such software. Presentations that were once typed and photocopied onto an overhead transparencies are now carefully prepared utilizing sophisticated software programs and printed on laser printers or on photographic slide film. More complex presentations, which may incorporate animated fades and dissolves between images, or even full motion video, may utilize a data processing system to drive a liquid crystal display (LCD) projection panel utilized with an overhead projector, or a three-gun cathode-ray tube (CRT) video projection system, or an LCD projection unit, each of which has the capability to produce full motion color images.
Even though many hours of time and much effort is utilized to produce such high quality presentations, many times the presentation is distorted when the images are projected on a projection surface, such as a wall or vertical screen. Such image distortion is often introduced by the relative placement of the projection system with respect to an axis normal to the projection surface at the center of the projected image. If an imaginary line drawn from the projection lens to the center of the projected image is not perpendicular (normal) to the surface on which the image is being projected, the image will appear distorted. Such image projection which is not normal to projection surface at the center of the projected image may be referred to as "off-axis projection." Consider, for example, the case in which a projection system is placed on a table and the image is projected onto a portion of a wall that is located above the level of the projection device. The image resulting from such projection will be wider at the top of the image than at the bottom of the image; a form of rectilinear distortion which may be referred to as a "keystone" distortion.
In a typical projection system, an image source S, which may be slide film, an overhead transparency or an LCD panel, is located between a condensing lens system and an objective. The condensing lens system captures divergent light rays from a concentrated source of light, and the objective lens, or lens system, forms an enlarged, inverted image of S upon a distant projection surface, such as a wall or screen. The ratio of enlargement, or magnifying power, M, of a projection system depends upon the distance D from the source S to the projection surface and the focal length f of the objective: M=(D-f)/f. Therefore the magnifying power is directly proportional to the distance D from the image source S to the projection surface; that is, the further the image is projected before being reflected from the projection surface, the larger the image will appear.
Thus, the image is larger near the top of the projected image and smaller near the bottom of the projected image because, in the case where the image is projected above the level of the projection system onto a vertical wall, the distance from the image source to the projection surface at the top of the image is longer, which produces a greater magnification near the top part of the image, than the distance from the image source to the projection surface at the bottom of the image, which produces a lesser magnification near the bottom of the image.
It should therefore be apparent that a need exist for a method and system which compensates for distortion, which results from off-axis projection of an image source, and thereby produces a more distortion free projected image.